In the interests of improving engine performance and fuel economy while reducing undesirable emissions, internal combustion engines are being designed to improve the mixing of intake air and injected fuel in the combustion chamber and to direct the flow of air and air-fuel mixture in order to provide an optimum mixture at the spark plug for ignition. In stratified charge spark-ignited engines, the air-fuel mixture is typically prepared in a non-homogeneous fashion to produce a relatively rich mixture at the spark plug while the remainder of the mixture is relatively lean. For this purpose, various approaches have been used such as incorporating tumble and/or swirl flows of air in the combustion chamber, and the use of various shaped recesses or bowls in the upper surface of the pistons. Changing the placement and/or orientation of the fuel injectors has also been used to provide improved engine performance.
As the rich mixture ignites around the spark plug, it in turn ignites the lean mixture in the main chamber. In such engines, therefore, the air-fuel mixture can be burned completely even if the air-fuel mixture, as a whole, is lean. Accordingly, fuel economy can be improved and gaseous emissions, such as nitrous oxide and carbon monoxide, contained in the exhaust and engine can be reduced.
It is known that combustion in an internal combustion engine can be improved by controlling the amount of turbulence within the combustion chamber. Various mechanisms have been used to introduce certain motion to the air and fuel within the cylinder. Due to the various geometries and structure of some of the engines, however, it is difficult to achieve the requisite tumble and/or swirl-types of air and air-fuel flows in the combustion chamber with some engines.
As a result, a need exists for securing tumble and/or swirl flows of air in certain internal combustion engines in order to produce beneficial charge stratification and improved engine performance and fuel economy while at the same time reducing undesirable emissions.